Diauxie

With diauxie (from the Greek di = two Auxano multiply, two growing ) refers to a two-phase growth of chemotrophic microorganisms in the presence of two different energy sources.

If two usable by the organism energy sources available simultaneously, at first only a diauxie is recycled. Here, the metabolism of the reduction of the second is switched off until the first one is completely consumed. After dismantling, the first energy source takes some time until the metabolism of the second begins. It follows a short growth arrest, which is called the lag phase.

At the physiological level, the diauxie is explained by catabolite repression: the one energy source whose utilization is easier because it is less enzymes are needed as in the exploitation of others, causes repression of the formation of those enzymes which are specifically required to build the second energy source. Only when the first source of energy is consumed, the education required for the degradation of the second power source is induced enzymes (so-called substrate induction). For example, the glucose -degrading enzymes in the bacterium Escherichia coli constantly producing and not subject to substrate induction. The enzymes specifically required for the breakdown of lactose, however, only be formed when glucose is consumed. Therefore, in most cases, the growth is faster than glucose with other sugars (glucose effect). At the genetic level is based on the diauxie both a negative and a positive control. In this context, the lactose operon has been described in great detail in the genome of Escherichia coli.

Lactose as an energy source, the time period between two consecutive partitions (doubling time) is approximately twice as long as for glucose in Escherichia coli. The enabled by lactose increase in bacterial mass is therefore significantly slower than with glucose as an energy source.

• Bacteriology